This application claims the priority right under 35 U.S.C. 119 of Japanese Patent Application No. Hei 10-341058 filed on Nov. 14, 1998, the entire disclosure of which is incorporated by reference.
(1) Field of the Invention
The present invention relates to an X-ray mask blank and a method for manufacturing the same, and an X-ray mask and a method for manufacturing the same.
(2) Description of the Related Art
In the semiconductor industry, as a conventional transfer technique of a fine pattern necessary for preparing an integrated circuit formed of the fine pattern on a silicon substrate, and the like, a photolithography method of using visible or ultraviolet rays as exposure electromagnetic waves to transfer the fine pattern has been used.
In recent years, however, with a progress of semiconductor technique, high integration of semiconductor devices such as an ultra LSI has remarkably progressed, and there arises a demand for a transfer technique of the fine pattern with high precision which exceeds a transfer limit in the visible or ultraviolet rays used in the conventional photolithography method.
In order to realize the transfer of such fine pattern, the development and practical application of an X-ray lithography method using X-rays shorter in wavelength than the visible or ultraviolet rays have been advanced.
X-ray lithography is an equal-size vicinity exposure, and requires an equal-size X-ray mask. The structure of the X-ray mask for use in the X-ray lithography is shown in FIG. 1.
As shown in FIG. 1, an X-ray mask 1 is constituted of an X-ray transmission film (membrane) 12 for transmitting X-rays, and an X-ray absorber pattern 13a for absorbing the X-rays, which are supported by a support substrate (support frame) 11a formed of silicon. Furthermore, to facilitate the reinforcing and handling, a glass frame 15 having a larger outer diameter than that of the support substrate is bonded to the support substrate. Here, for example, the support substrate with an outer diameter of four inches, and the glass frame with an outer diameter of five inches are used.
A process of preparing an X-ray mask blank to obtain the X-ray mask is shown in FIG. 2.
First, the X-ray transmission film 12 with a thickness of about 2 xcexcm is formed on both surfaces of a silicon substrate 11 by CVD method, and subsequently an X-ray absorbing film 13 and an etching mask layer 14 are successively formed on the X-ray transmission film 12 by a sputtering method (FIG. 2a).
Subsequently, an area to form a mask area is removed from the X-ray transmission film (not shown) formed on the back surface of the substrate by dry etching, the X-ray transmission film remaining on an outer peripheral portion is used as a mask to wet-etch the central portion of the back surface of the silicon substrate by hydrofluoric nitrate (mixed solution of hydrofluoric acid and nitric acid) until the back surface of the X-ray transmission film 12 is exposed, and the X-ray transmission film 12 is self-supported (formed into a membrane) (FIG. 2b).
Next, the reinforcing glass frame 15 is bonded by a method such as anodic bonding (FIG. 2c).
As the X-ray transmission film 12, silicon carbide or another material which has a high Young""s modulus and a superior resistance against X-ray radiation is generally used. As the X-ray absorbing film 13, a material containing tantalum (Ta), tungsten (W), and the like which has a high X-ray absorbing ratio and a superior resistance against X-ray radiation is well used.
In recent years, with the progress of the photolithography technique, the time to introduce the X-ray lithography is fed forward, and in the present situation, the lithography is expected to be introduced from the generation of 1 Gbit-DRAM (design rule: 0.18 xcexcm). Even if the X-ray lithography is introduced from 1 G, it can be used over a plurality of generations of 4 G. 16 G, 64 G. As the generation advances, strict prescribed properties are required.
Particularly, the X-ray absorbing film is requested to have a high X-ray absorbing ratio, to have a dense crystalline structure to provide an excellent dry etching property and form smooth pattern side walls and upper face, to be able to form a pattern of 0.18 xcexcm or less and enhance the dimensional precision of the pattern, to have a low stress and no stress nonuniformity, to have no pattern strain or positional fluctuation caused by the stress or stress change and be superior in positional precision, to be superior in X-ray radiation resistance, and to have other strict prescribed properties.
For the positional precision required for the X-ray mask, for example, when the use in 64 G is assumed, the precision becomes stricter, and a high positional precision of 10 nm is necessary. Therefore, the strain attributed to the film stress needs to be as close to zero as possible. Particularly, it is important to minimize the pattern strain attributed to the stress of the X-ray absorbing film. The X-ray absorbing film needs to have an excessively low stress, and to be uniform in a mask area. For example, in the X-ray absorbing film with a thickness of 0.5 xcexcm, a stress of xc2x110 MPa or less is required in the mask area of 30 mm square.
Additionally, the stress of the prepared film has to be unchanged and maintained even after the pattern is formed to prepare the mask. If the stress of the film forming the pattern changes, the pattern strain is caused after preparing the mask, which raises a problem.
The present invention has been developed under the above-described background, and a first object thereof is to provide an X-ray mask blank from which an X-ray mask satisfying strict prescribed properties requested for X-ray masks of 1 Gbit-DRAM and subsequent generations can be manufactured, a method for manufacturing the blank, a method for manufacturing the X-ray mask, and the like.
Another object is to provide an X-ray mask which satisfies strict prescribed properties requested for X-ray masks of 1 Gbit-DRAM and subsequent generations, and particularly a second object is to provide an X-ray mask which has no pattern strain or no positional fluctuation attributed to a change of film stress of an X-ray absorber pattern after preparing the mask and which is superior in positional precision.
To achieve the above-described objects, as a result of intensive researches, the present inventors have found that an X-ray absorbing film containing tantalum (Ta), boron (B), nitrogen and/or oxygen has a high X-ray absorbing ratio, has a dense crystalline structure to provide an excellent dry etching property and form smooth pattern side walls and upper face, can form a pattern of 0.18 xcexcm or less to enhance a pattern dimensional precision, has a low stress and no stress nonuniformity, has no pattern strain or no positional fluctuation attributed to the stress and stress change to provide a superior positional precision, is superior in X-ray radiation resistance, and satisfies strict prescribed properties required for X-ray masks of 1 Gbit-DRAM and subsequent generations.
Specifically, the present invention is constituted as follows:
(Constitution 1) An X-ray mask blank comprising, on a mask substrate, an X-ray transmission film for transmitting X-rays and an X-ray absorbing film formed on the X-ray transmission film for absorbing the X-rays, the X-ray absorbing film containing tantalum, boron and nitrogen.
(Constitution 2) An X-ray mask blank comprising, on a mask substrate, an X-ray transmission film for transmitting X-rays and an X-ray absorbing film formed on the X-ray transmission film for absorbing the X-rays, the X-ray absorbing film containing tantalum, boron and oxygen.
(Constitution 3) An X-ray mask blank comprising, on a mask substrate, an X-ray transmission film for transmitting X-rays and an X-ray absorbing film formed on the X-ray transmission film for absorbing the X-rays, the X-ray absorbing film containing tantalum, boron, nitrogen and oxygen.
(Constitution 4) A method for manufacturing an X-ray mask blank, comprising steps of forming an X-ray transmission film on a mask substrate, and forming an X-ray absorbing film on the X-ray transmission film, the step of forming the X-ray absorbing film comprising steps of using a target containing tantalum and boron, and adding gas containing nitrogen and/or gas containing oxygen to sputtering gas to form the X-ray absorbing film.
(Constitution 5) An X-ray mask comprising, on a support substrate, an X-ray transmission film for transmitting X-rays and an X-ray absorber pattern formed on the X-ray transmission film for absorbing the X-rays, the X-ray absorber pattern comprising a material containing tantalum, boron, nitrogen and/or oxygen.
In the present invention the X-ray absorbing film containing tantalum (Ta), boron (B), nitrogen and/or oxygen has a: high X-ray absorbing ratio, has a dense crystalline structure to provide an excellent dry etching property and form smooth pattern side walls and upper face, can form a pattern of 0.18 xcexcm or less to enhance a pattern dimensional precision, has a low stress and no stress nonuniformity, has no pattern strain or no positional fluctuation attributed to the stress and stress change to be superior in positional precision, is further superior in X-ray radiation resistance, and satisfies strict prescribed properties required for the X-ray masks of 1 Gbit-DRAM and subsequent generations.
Particularly, when the X-ray absorbing film is dry-etched to form the X-ray absorber pattern, the pattern side face is exposed as a new face of the X-ray absorbing film, but in the X-ray absorbing film containing tantalum (Ta), boron (B), nitrogen and/or oxygen, the pattern side face is not substantially oxidized in atmosphere even after the X-ray absorber pattern is formed, so that the change of the film stress of the X-ray absorber pattern by the oxidation of the pattern side face can be minimized. Therefore, the film has no pattern strain or no positional fluctuation attributed to the stress change after the formation of the X-ray absorber pattern, and is superior in positional precision. On the other hand, when the X-ray absorbing film is formed of pure metals such as Ta, W, or alloys mainly containing Ta or W, the pattern side face is oxidized in the atmosphere after the formation of the X-ray absorber pattern, so that the formed oxide film easily generates the film stress change of the X-ray absorber pattern and the stress change amount is large. Moreover, even in the compound of Ta and B, the stress change of about 5 MPa is generated by the surface oxidation, and the mask having a design rule of 0.18 xcexcm is strained by 30 nm at maximum.
Moreover, the X-ray absorbing film containing tantalum (Ta), boron (B), nitrogen and/or oxygen generates no stress change even during cleaning using the mixed solution of sulfuric acid and aqueous hydrogen peroxide, and the like. Therefore, the film has no pattern strain or no positional fluctuation attributed to the stress change after the pattern formation and is superior in positional precision.
Furthermore, the X-ray absorbing film containing tantalum (Ta), boron (B), nitrogen and/or oxygen has a high X-ray absorbing ratio and a dense crystalline structure, so that the dry etching property is excellent and the pattern side walls and upper face are smooth. Additionally, the film can form a pattern of 0.18 xcexcm or less to enhance the pattern dimensional precision, and has a low stress and no stress nonuniformity.
Additionally, the present invention is suitable for the manufacture of the X-ray masks of 1 Gbit-DRAM and subsequent generations, and also suitable for the manufacture of the X-ray masks of 4 Gbit-DRAM (design rule of 0.13 xcexcm) and subsequent generations.